Documentation: perf: Update documentation for ThunderX2 PMU uncore driver

Add documentation for Cavium Coherent Processor Interconnect (CCPI2) PMU.

Signed-off-by: Ganapatrao Prabhakerrao Kulkarni <[e-mail]>
Signed-off-by: Will Deacon <[e-mail]>

Documentation/admin-guide/perf/thunderx2-pmu.rst

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 The ThunderX2 SoC PMU consists of independent, system-wide, per-socket
-PMUs such as the Level 3 Cache (L3C) and DDR4 Memory Controller (DMC).
+PMUs such as the Level 3 Cache (L3C), DDR4 Memory Controller (DMC) and
+Cavium Coherent Processor Interconnect (CCPI2).
 
 The DMC has 8 interleaved channels and the L3C has 16 interleaved tiles.
 Events are counted for the default channel (i.e. channel 0) and prorated
 to the total number of channels/tiles.
 
-The DMC and L3C support up to 4 counters. Counters are independently
-programmable and can be started and stopped individually. Each counter
-can be set to a different event. Counters are 32-bit and do not support
-an overflow interrupt; they are read every 2 seconds.
+The DMC and L3C support up to 4 counters, while the CCPI2 supports up to 8
+counters. Counters are independently programmable to different events and
+can be started and stopped individually. None of the counters support an
+overflow interrupt. DMC and L3C counters are 32-bit and read every 2 seconds.
+The CCPI2 counters are 64-bit and assumed not to overflow in normal operation.
 
 PMU UNCORE (perf) driver:
 
 The thunderx2_pmu driver registers per-socket perf PMUs for the DMC and
-L3C devices.  Each PMU can be used to count up to 4 events
-simultaneously. The PMUs provide a description of their available events
-and configuration options under sysfs, see
-/sys/devices/uncore_<l3c_S/dmc_S/>; S is the socket id.
+L3C devices.  Each PMU can be used to count up to 4 (DMC/L3C) or up to 8
+(CCPI2) events simultaneously. The PMUs provide a description of their
+available events and configuration options under sysfs, see
+/sys/devices/uncore_<l3c_S/dmc_S/ccpi2_S/>; S is the socket id.
 
 The driver does not support sampling, therefore "perf record" will not
 work. Per-task perf sessions are also not supported.